Different pressure amplitudes at co-located source and sensors

I am running the "example_tvsp_homogeneous_medium_monopole.m" example with co-located source and sensor positions:

source.p_mask(64,64) = 1;
sensor.mask(64,64) = 1;

Ideally, I would expect exact same amplitudes of both pressure curves (Input Pressure Signal and Sensor Pressure Signal) but what I get is attenuated pressure at sensor with following root mean square values:

When you define a pressure source in k-Wave, you are specifying an injection of mass which adds to the pressure already in the medium. The output is the solution the wave equation given this time varying source, which won't be the same.